Endocrine Abstracts

There is increasing evidence that alterations in alternative splicing can be linked to key tumor features in cancer. Dysregulations in the splicing machinery constitute the underlying cause in many of these alterations and, consequently, splicing and its control are emerging as a novel and transversal cancer hallmark, due to its association with different dysfunctions of tumor cells. In line with this, we discovered the existence of aberrantly spliced variants of somatostatin receptor 5 (SST₅TMD4) and ghrelin (In1-ghrelin), which are overexpressed and linked to malignancy features in pancreatic neuroendocrine tumors (PNETs). In this study, we aimed at characterizing the pattern of expression of pivotal components of the splicing machinery, its potential dysregulation and its relation with aggressiveness of PNETs, with the ultimate goal of identifying novel, useful biomarkers for diagnostic and treatment of these tumors. To this end, we designed an array that allowed to determine the expression levels of 45 splicing machinery components using a microfluidic-based technology in 20 pancreatic NETs samples and their control-adjacent non-tumoral tissues. This revealed that the expression of several splicing factors and spliceosome components was altered in tumor tissue compared to non-tumoral adjacent tissue, suggesting a profound dysregulation of the splicing machinery in PNETs. Then, we selected one of the most altered components, NOVA1, to explore its properties in two PNETs model cell lines, BON-1 and QGP-1, by measuring signaling pathways and aggressiveness features, including proliferation and growth of xenografted tumors in mice. This showed that levels of NOVA1, a splicing factor highly overexpressed in tumors, correlated with relevant clinical features, including higher Ki-67 index and necrosis. In vitro assays in BON-1 and QGP-1 cell lines demonstrated that NOVA1 overexpression increased cell proliferation; conversely, NOVA1 silencing markedly decreased cell proliferation. Interestingly, overexpression or silencing of NOVA1 led to opposite changes in the activation/inhibition of key signaling pathways and in the expression of key molecular markers. Of note, alteration of NOVA1 in these cells affected their responsiveness to everolimus in terms of proliferation. Finally, NOVA1 overexpression increased the growth of BON-1 xenografted tumors in nude mice. These results demonstrate that splicing is altered in PNETs, and provide compelling evidence for a role of the splicing factor NOVA1 in PNETs oncogenesis and aggressiveness, thus paving the way to explore its possible value as a biomarker and therapeutic target in PNETs.